Metallographic diagram of 40Cr (1100℃×20min+470℃×1s water cooling)

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The purpose of this report is to investigate and analyse the microstructural characteristics of a 40Cr specimen after having been processed with a heat treatment of 1100°C for 20 minutes followed by a water quench at 470°C for 1s.

Microstructural assessment of steel components plays an important role in its properties as well as fatigue resistance. Giant Stride Microscope (GSM) is utilised to obtain the neccessary images of the specimens, which can then be further analysed.

To begin with, the specimens are polished and etched in order to obtain smooth surface for image acquisition. This specimen is etched with an aqueous solution of 2.5g nital per 100ml ethanol by weight. After this the specimen is mounted on a copper planchet, aligned with the test surface upwards then left for 3 to 4 minutes in the etching solution.

Once this is finished the specimens are examined in the GSM, LED lighting is used in order to achieve the brightest image and reduce any confusion or false signals when distinguishing the microstructures. The magnification of the microscope is set to x400 in order to get a clearer picture.

Once the micrograph was obtained, it was analysed to investigate the microstructure of the specimen. It can be observed that the matrix is composed primarily of small discrete pearlite colonies, with small amounts of ferrite present. The edges of the individual pearlite colonies have a significant amount of fine bainite present. Overall, the microstructural characteristics of this specimen are consistent with what is expected for the 40Cr alloy after having been processed with the specified heat treatment.

In conclusion, this report has discussed the microstructural characteristics of a 40Cr specimen after being processed with a heat treatment of 1100°C for 20 minutes followed by a water quenching at 470°C for 1s. The microstructure was investigated using a Giant Stride Microscope and it was observed that the matrix is composed primarily of small discrete pearlite colonies, with small amounts of ferrite present. The edges of the individual pearlite colonies have a significant amount of fine bainite present.

Microstructure Analysis of 40Cr After Heat Treatment of 1100°C for 20 Minutes Followed by Quenching at 470°C for 1 Second

The present paper discusses the microstructure analysis of the alloy steel 40Cr after a heat treatment of 1100°C for 20 minutes followed by quenching at 470°C for 1 second. The microstructures were observed in the optical microscope with polarized light and were found to consist of two phases, ferrite and martensite.

The ferrite phase was seen to exist as an elongated polygonal pattern and occupied approximately 42% of the total area of the microstructure sample. This phase had the size range of 5-30 µm, with a maximum area fraction of 42%. The surface was found to be smooth with porosity equal to 0%. It is also believed that the ferrite was affected by the hardness of the alloy but it is not known to what extent.

The other phase present in the sample was martensite. It was observed to have a fine microstructure with a size range of 0.2 to 0.5 microns and a maximum area fraction of 58%. The surface was seen to have a coarse finish with some minute porosity on the surface.

The presence of these two phases holds great importance for understanding the behavior of the alloy steel. It is believed that the ferrite phase present in the microstructure contributes to the strength of the material due to its hardness. Whereas, the martensite phase is known to impart ductility and toughness to the material which makes it ideal for use in automotive and other applications that require good strength and flexibility.

In conclusion, the microstructure analysis revealed that the heat treatment at 1100°C followed by water quenching at 470°C produced two phases, ferrite and martensite, with size ranges of 5-30 µm and 0.2 to 0.5 microns, respectively. The ferrite phase contributed to the strength of the alloy while the martensite phase contributed to its ductility and toughness.